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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | ||||
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | ||||
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | ||||
.\" SUCH DAMAGE. | .\" SUCH DAMAGE. | ||||
.\" | .\" | ||||
.\" From: @(#)tcp.4 8.1 (Berkeley) 6/5/93 | .\" From: @(#)tcp.4 8.1 (Berkeley) 6/5/93 | ||||
.\" $FreeBSD$ | .\" $FreeBSD$ | ||||
.\" | .\" | ||||
.Dd January 14, 2021 | .Dd February 11, 2021 | ||||
.Dt TCP 4 | .Dt TCP 4 | ||||
.Os | .Os | ||||
.Sh NAME | .Sh NAME | ||||
.Nm tcp | .Nm tcp | ||||
.Nd Internet Transmission Control Protocol | .Nd Internet Transmission Control Protocol | ||||
.Sh SYNOPSIS | .Sh SYNOPSIS | ||||
.In sys/types.h | .In sys/types.h | ||||
.In sys/socket.h | .In sys/socket.h | ||||
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Large bursts can cause buffer overruns and packet drops if routers have small | Large bursts can cause buffer overruns and packet drops if routers have small | ||||
buffers or the link is experiencing congestion. | buffers or the link is experiencing congestion. | ||||
.It Va newcwd | .It Va newcwd | ||||
Enable the New Congestion Window Validation mechanism as described in RFC 7661. | Enable the New Congestion Window Validation mechanism as described in RFC 7661. | ||||
This gently reduces the congestion window during periods, where TCP is | This gently reduces the congestion window during periods, where TCP is | ||||
application limited and the network bandwidth is not utilized completely. | application limited and the network bandwidth is not utilized completely. | ||||
That prevents self-inflicted packet losses once the application starts to | That prevents self-inflicted packet losses once the application starts to | ||||
transmit data at a higher speed. | transmit data at a higher speed. | ||||
.It Va do_prr | |||||
Perform SACK loss recovery using the Proportional Rate Reduction (PRR) algorithm | |||||
described in RFC6937. | |||||
This improves the effectiveness of retransmissions particular in environments | |||||
with ACK thinning or burst loss events, as chances to run out of the ACK clock | |||||
are reduced, preventing lengthy and performance reducing RTO based loss recovery | |||||
(default is true). | |||||
.It Va do_prr_conservative | |||||
While doing Proportional Rate Reduction, remain strictly in a packet conserving | |||||
mode, sending only one new packet for each ACK received. | |||||
Helpful when a misconfigured token bucket traffic policer causes persistent | |||||
high losses leading to RTO, but reduces PRR effectiveness in more common settings | |||||
(default is false). | |||||
.It Va rfc6675_pipe | .It Va rfc6675_pipe | ||||
Calculate the bytes in flight using the algorithm described in RFC 6675, and | Calculate the bytes in flight using the algorithm described in RFC 6675, and | ||||
is also a prerequisite to enable Proportional Rate Reduction. | is also an improvement when Proportional Rate Reduction is enabled. | ||||
.It Va rfc3042 | .It Va rfc3042 | ||||
Enable the Limited Transmit algorithm as described in RFC 3042. | Enable the Limited Transmit algorithm as described in RFC 3042. | ||||
It helps avoid timeouts on lossy links and also when the congestion window | It helps avoid timeouts on lossy links and also when the congestion window | ||||
is small, as happens on short transfers. | is small, as happens on short transfers. | ||||
.It Va rfc3390 | .It Va rfc3390 | ||||
Enable support for RFC 3390, which allows for a variable-sized | Enable support for RFC 3390, which allows for a variable-sized | ||||
starting congestion window on new connections, depending on the | starting congestion window on new connections, depending on the | ||||
maximum segment size. | maximum segment size. | ||||
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